In means for actuating drive apparatuses it is repeatedly the case that a delayed reaction to an actuation process has to be accepted owing to a response delay which is caused by a control element for the drive apparatus. Apart from, for example, compressed-air-actuated drive apparatuses with pneumatic control valves, which can introduce such a response delay, this also applies to inductive actuators, generally actuators with switching delays. A quite specific example are drive apparatuses with an electric motor for moving components in motor vehicles (Kfz), with automatic operation, such as for example window lifters, sunroofs, and also tailgates, sliding doors and similar components. In the means for actuating the electromagnetic drive apparatuses which are provided here, switching relays are generally used and this applies, generally to many controllers for electric motors. Specifically when a reversal of direction is provided for the motor, relays are used for energizing the motors, also for reasons of cost.
In the motor vehicle components mentioned above, such as for example window lifters with automatic operation, an anti-trapping means is frequently provided, which requires the rapid reversal of the rotational direction, or the rapid reversal of the polarity of the electric motor which this requires, when a trapping situation is detected. Such an anti-trapping means is usually implemented using computer means, for example a correspondingly programmed microprocessor or microcomputer, which then actuate a relay as a control element. Switching relays are known to require a certain time to allow an actuation (stimulation) to follow a reaction (switching). These delay times can then easily be accepted, or it is attempted to make an early detection or early decision by means of the software, if an event can be evaluated as “trapping”. For example, the force threshold value with which the current closing force is compared could be defined as being basically lower than is actually justified, in order therefore to be able to make a correspondingly early decision about a trapping situation. However, in such a case it may subsequently be found that the force drops again before the actual threshold value is reached and in fact a trapping situation has not occurred, and that the reaction with reversing the motor is therefore incorrect. As a result, uncertainties and low levels of robustness in the systems affected arise when the intention is to compensate the above-mentioned delay times in this way.